Biochem Genetics DNA Replication - Comp Exam Study guide.txt

• 1. mechanism must exist for DNA to unwind and be STABLE in open position: helicase and ssBP
• 2. Unwinding and synthesis create tension further down helix which needs to be reduced: topoisomerases
• 3. Primer needs to be synthesized for polymerization to start: primase
• 4. Both strands synthesized simultaneously, but in different manners (continuous w/leading and lagging): DNA polymerase III, replisome, okazaki fragments
• 5. RNA primer must be removed prior to completion of replication: DNA polymerase I
• 6. Gaps between strands must be filled: ligase
• 7. DNA needs to be proofread for errors: DNA polymerase I and III

Telomerase: binds to the end GGTTT sequences with complementary bps, allowing the 3í end DNA template to NOT create the hairpin loop, thereby allowing the complementary strand to FINISH replication

• circular shape molecule, up to few mil. bps
• SINGLE origin of replication
• replication BIdirectional
• Both strands replicated simultaneously
• meeting/terminating at ter sites, producing 2 circular molecules
• about 20min

• MULTIPLE LINEAR DNA molecules (1 per chromosome), each millions of bps
• Multiple ori's
• need special mechanisms to fully replicate ENDS of each molecule
• several hours

• 1)Helicases unstabalize the helix opening up the DNA
• 2) Single strand binding protiens hold the helix in the open position
• 3) Topoisomerases (DNA Gyrase) relieves tension from supercoiling ahead of the helix
• 4) Primase ñ Synthesizes and lays down an RNA primer so DNA polymerase can begin synthesizing DNA
• 5) DNA Polymerase III begins synthesizing new DNA in the 5í-3í Direction
• 6) Leading strand is direct but lagging strand done in small pieces ñ Okazaki fragments
• 7) DNA polymerase I ñ removes RNA primers and fills in space with DNA
• 8) DNA Ligase joins the phosphate backbones of the various fragments (fills in the nicks)
• 9) All DNA polymerase contain 3í-5í exonuclease activity allowing for proofreading and synthesizing of DNA in 5í-3í direction

• ◦ The role of SSBP:
• 1. Protect ssDNA from degradation.
• 2. Control what proteins have access to the ssDNA.
• 3. Aid helicases by stabilizing the unwound ssDNA.
• 4. ssDNA can bond to itself forming hairpin helices. SSB prevent formation of the hairpin helices that impede synthesis by DNA polymerase. They exhibit cooperative binding on the ss-lagging strand of the DNA.

• Initiation is the first step in translation
• 1. begins with METHIONINE
• 2. NO Shine-Dalgarno sequence
• 3. mRNA HAS 5' CAP
• 4. 12 Initiation factors

1. N-formyl-methionine2. HAS Shine-Dalgarno sequence (Shows ribosomes where to start)3. Has Initiation factors 1, 2 & 3